Explaining all-optical switching in ferrimagnets with heavy rare-earth elements by varying the spin-flip scattering probability of Gd in Co${}_x$Gd${}_{100-x}$ alloys and Co/Gd bilayers

Using the microscopic three temperature model, we simulate single-pulse all-optical switching (AOS) in alloys and bilayers consisting of Co and Gd. In particular, we investigate its dependence on the spin-flip probability of Gd $a_{\mathrm{s}\mathrm{f},\mathrm{G}\mathrm{d}}$, a material parameter describing the strength of spin-phonon coupling. We do so to elucidate the mechanisms behind all-optical switching in systems where Co is coupled to heavy rare-earth elements with higher damping such as Tb. In alloys, our observations are twofold. First, an increase of $a_{\mathrm{s}\mathrm{f},\mathrm{G}\mathrm{d}}$ leads to a broadening of the range of compositions for which AOS is observed. Second, the ideal Co content is decreased as $a_{\mathrm{s}\mathrm{f},\mathrm{G}\mathrm{d}}$ is varied. For bilayers, our analysis indicates that switching is most efficient when $a_{\mathrm{s}\mathrm{f},\mathrm{G}\mathrm{d}}$ takes on small values. Conversely, increasing the value of $a_{\mathrm{s}\mathrm{f},\mathrm{G}\mathrm{d}}$ leads to a general suppression of AOS. Comparing alloys to bilayers, we find that AOS in alloys exhibits greater resilience to variations in $a_{\mathrm{s}\mathrm{f},\mathrm{G}\mathrm{d}}$ than it does in bilayers.